1. Field of the Invention
The present invention relates generally to an electrically-operated sealed compressor such as, for example, a scroll compressor or a rotary compressor for use in air conditioners, refrigerators or the like and, more particularly, to a gear pump mounted in the electrically-operated sealed compressor.
2. Description of Related Art
Conventionally, an electrically-operated sealed compressor such as a scroll compressor or a rotary compressor is generally used in a cooling apparatus for air conditioners, refrigerators, or the like. This kind of conventional compressor is discussed hereinafter taking the case of a scroll compressor.
As shown in FIG. 14, a sealed vessel 10 accommodates a compression mechanism 1, an electric motor 7 including a stator 5 and a rotor 6, a crankshaft 2 for transmitting the rotational force of the electric motor 7 to the compression mechanism 1, a main bearing 3 for supporting one end of the crankshaft 2, and an auxiliary bearing 4a having a bearing holder 4 for supporting the other end of the crankshaft 2. The main bearing 3 has a container 11 attached thereto for temporarily collecting oil which has been supplied to the bearing portions for lubrication thereof. The sealed vessel 10 is provided with a suction pipe 8 for sucking in a low-pressure refrigerant gas and a discharge pipe 9 for discharging a high-pressure refrigerant gas compressed by the compression mechanism 1 to the outside of the sealed vessel 10. The crankshaft 2 has a gear pump 150 attached to the end thereof which is supported by the auxiliary bearing 4a.
In the above-described construction, when the rotor 6 of the electric motor 7 rotates, the rotational force thereof is transmitted to the compression mechanism 1 by the crankshaft 2, to thereby compress a refrigerant gas. More specifically, the compression mechanism 1 compresses the low-pressure refrigerant gas drawn through the suction pipe 8 into a high-pressure refrigerant gas, which is in turn discharged into a discharge side space 14 defined in the sealed vessel 10. Thereafter, the high-pressure refrigerant gas passes through a communication hole 12 defined in the main bearing 3 and enters an electric motor side space 17. The main current of the high-pressure refrigerant gas passes through a cutout defined in the stator 5 and enters an auxiliary bearing side space 18 before it is eventually discharged into a refrigerating cycle (not shown) through the discharge pipe 9.
On the other hand, the gear pump 150 has a pump casing 151 including a pair of gears 52, a strainer 157, a foreign substance storage chamber 155 for storing foreign substances captured by the strainer 157, and an oil suction nozzle 156. The pump casing 151 is covered with a cover plate 153 fastened thereto by a plurality of, for example four, screws 152, and has a recess 60a defined therein so that a gear chamber 60 for accommodating the gear pair 52 therein may be formed by the cover plate 153 and the recess 60a. The fastening force of the screws 152 maintains the tightness between the pump casing 151 and the cover plate 153 to ensure sealing properties to the oil and the refrigerant gas.
As shown in FIGS. 15 and 16, the pump casing 151 has an oil well 61 defined therein and adjoining the gear chamber 60 so that the gear pair 52 may be supplied with the oil which serves as lubricating and sealing oil at the starting of the pump. The strainer 157 comprises a stainless screen 157a sandwiched between two stainless frames 157b and spot-welded thereto, and a plurality of elastic members or pieces 157c protruding therefrom. As shown in FIG. 16, when the strainer 157 is mounted in the pump casing 151, the elastic members 157c act to bias the strainer 157 against its mounting surface on the pump casing 151 to prevent the foreign substances in the foreign substance storage chamber 155 from entering the gear chamber 60.
The gear pump 150 has an insert formed thereon and inserted into an associated portion of the bearing holder 4, and the pump casing 151 is fastened to its seat formed on the bearing holder 4 by a plurality of (for example, two) bolts 154. As shown in FIG. 15, the gear pair 52 is comprised of an outer gear 52a and an inner gear 52b in mesh with each other. That end of the crankshaft 2 to which the gear pump 150 is attached has a cutout so as to present a generally D-shaped section and is inserted into a center hole of an inner gear 52b having a corresponding shape. The driving force of the electric motor 7 is transmitted to the inner gear 52b via the D-shaped portion of the crankshaft 2 and that of the inner gear 52b to cause the outer and inner gears 52a and 52b to undergo a mutual rotation for pumping action.
When the compressor is in operation, the lubricating oil in an oil sump 15 formed at a lower portion of the sealed vessel 10 is sucked up into the inside of the gear pump 150 through the oil suction nozzle 156, and is then introduced into the space defined between the outer and inner gears 52a and 52b after having passed through the strainer 157 for filtering of foreign substances contained therein. Thereafter, the lubricating oil is fed into an oil passage 153b defined in the cover plate 153 by the pumping action of the gear pair 52, passes through a through-hole defined in the crankshaft 2 along the center line thereof, and is fed to the compression mechanism 1. Most of the lubricating oil acts to lubricate the sliding surfaces of the main bearing 3 and the crankshaft 2 and is then collected in the oil collecting container 11 attached to the main bearing 3. The lubricating oil thus collected in the container 11 is discharged therefrom through a discharge port 11a defined therein and drops by its own gravity to return to the oil sump 15 formed at the lower portion of the sealed vessel 10. The remaining oil together with the high-pressure refrigerant gas is discharged from the compression mechanism 1 into the sealed vessel 10 and is separated from the high-pressure refrigerant gas during movement thereof inside the compressor. This lubricating oil also drops by its own gravity to return to the oil sump 15.
According to the above-described conventional compressor, however, because the pump casing includes the strainer, the foreign substance storage chamber, and the oil suction nozzle in addition to the gear pair, the height of the pump casing becomes large in the longitudinal direction of the compressor. The height depends on the size required for mounting the strainer, the size appropriate to the volume required for the foreign substance storage chamber, and the size appropriate to the diameter of the oil suction nozzle. On the other hand, the gear chamber accommodating the gear pair and formed in the pump casing is covered with the cover plate screwed to the pump casing, thus inevitably elongating the total longitudinal length of the bearing holder and the gear pair.
For these reasons, in the event that the crankshaft undergoes a whirling motion having tilted from the ideal axis of the crankshaft, the gear pair is also affected by the whirling motion of the crankshaft and will undergo an eccentric motion relative to the ideal axis of the crankshaft. More specifically, the inner and outer gears forming the gear pair rotate relative to each other with their gear teeth clashing against each other during rotation of the crankshaft that is then undergoing the whirling motion. Clashing of the gear teeth eventually leads to an abnormal wear of the gear teeth, the wall surface of the gear chamber, the driving portion of the crankshaft that is for driving the gear pair or the like. It may also generate abnormal sounds during operation of the compressor, resulting in a lowering in performance and also in reliability of the compressor.
To overcome this kind of problem, it is necessary for the conventional compressor to have a relatively large clearance between the gear pair and the gear chamber. In this case, however, the large clearance lowers the sealing properties between the gear pair and the gear chamber, thus reducing the performance of the pump in terms of flow rate and pump head. According to another method of overcoming the above problem, the crankshaft, the bearing holder, and the gear pump are combined with one another after the design tolerances thereof have been strictly determined. This method, however, requires not only highly accurate machining on these elements, but also very careful inspection and management thereof after the machining.
Furthermore, as described previously, because the conventional compressor is provided with the pump casing accommodating or having the strainer, the foreign substance storage chamber, and the oil suction nozzle in addition to the gear pair, the projected area of the pump casing becomes large in the longitudinal direction of the compressor. Also, the large height of the pump casing results in an enlargement in the volume of the entire gear pump.
On the other hand, to prevent the lubricating oil from being discharged, along with a flow of refrigerant gas, to the outside of the compressor, the auxiliary bearing side space is required to have a sufficiently large volume. For this reason, the gear pump should be a small-sized one of a small volume.
In view of this requirement, it is necessary to remove functionally unnecessary pads from the gear pump. To this end, the pump casing and the cover plate become complicated in shape, and screws are frequently used in fastening them. The fastening by the screws generates minute strains in the cover plate which in turn create a minute gap between the pump casing and the cover plate, resulting in lower sealing properties.
As a result, there arises the problem that the refrigerant gas may enter the gear pump, thus reducing the pump performance in terms of flow rate and then reducing the performance and reliability of the compressor.
On the other hand, when the operation of the compressor is stopped and the compressor is again started, the gear pair must be supplied with oil to ensure lubrication and sealing thereof for a sufficient pump head. To this end, an oil well is provided so as to adjoin the gear chamber in the pump casing, thus creating a discontinuous plane having a cutout on the cylindrical wall of the gear chamber. Accordingly, when the gear pair undergoes a rotating motion to provide a pumping effect, it slides relative to such cutout thereby causing an abnormal wear of the gear pair and the gear chamber. The worn-out powder (or shavings) thus generated reaches, together with an oil flow, the sliding portions of the compression mechanism and causes seizing thereof. This has a considerably bad influence on the performance and reliability of the compressor. Also, the sliding movement between the gear pair and the cutout generates noise during operation of the compressor.
Moreover, the conventional gear pump employs a screen of a rectangular shape. Accordingly, in an attempt to enhance the capability of capturing foreign substances contained in the oil by increasing the screen area, the total length around the strainer becomes longer as compared with an increase in screen area. As a result of this, the height of the pump casing becomes larger. As described previously, because the pump casing should be thin, a sufficient screen area cannot be ensured.
Also, because the strainer is caused to adhere to the pump casing by the action of the elastic members attached to and protruding from the strainer frame, the adhesive properties of the strainer to the pump casing vary according to a variation of the elastic force of the elastic members.
Furthermore, when the strainer is mounted in the pump casing, the strainer is first inserted into a strainer chamber in the pump casing and an insertion hole is subsequently covered with the cover plate. Because of this arrangement, it is likely that a gap is created between the strainer and the cover plate and, hence, the function of the strainer for capturing foreign substances in the oil cannot be completely attained. More specifically, of the foreign substances contained in the oil, very small ones are likely to pass through such gap and reach, along with an oil flow, the sliding portions of the compression mechanism. These very small foreign substances may cause seizing of the sliding portions, which has a very bad influence on the performance of the compressor.
In addition, because horizontal type electrically-operated compressors and vertical type ones differ in the arrangement of the oil sump within the sealed vessel, it is necessary to prepare gear pumps of different specifications wherein the position of an oil suction nozzle differs to ensure sufficient oil pumping from the oil sump up to the gear pump.